The present invention relates to variable gain amplifiers, and more particularly, to variable gain amplifiers including DC-compensation loops having a gain independent high pass filter cut off frequency.
A variable gain amplifier alters the gain of an input voltage signal based upon a provided input variable. Within microcircuit design, DC-offsets arc generated by variable gain amplifiers due to component mismatches. For higher gain amplifiers, it is necessary for the DC-offset to be removed. The DC-offset comprises a direct current level that is added to the input signal of the amplifier. The DC-offset of a variable gain amplifier may be removed by using DC blocking capacitors or DC feedback loops. However, for baseband frequency applications, capacitors are too large for integration within microcircuit amplifiers. For variable gain amplifier applications, conventional DC feedback loops causes a gain dependent cutoff frequency. Thus, there is a need for an improved method of DC-offset removal that does not suffer from the limitations of the prior art.
The present invention overcomes the foregoing and other problems with a variable gain amplifier having an input and an output with a DC-offset compensation loop connected between the input and output. The DC-offset compensation loop has a gain independent cut off frequency and removes DC-offsets from the output of the variable gain amplifier.